/* ==========================================================================
   CLEAR AIR — light, airy design system for zhuozheng.top

   Black + antique gold + Stanford Cardinal, with one job per colour so no
   hue is decoration:

     ink   (near-black)  structure and body copy
     accent(gold)        interactive + metadata — links, nav state, venue
                         pills, dates, resource chips
     signal(Cardinal)    identity and distinction — the name, Stanford, the
                         self-name in author lists, the job-market line,
                         recognition badges, honours
     mark  (black chip)  software artifacts, distinct from research output
   ========================================================================== */

:root {
  --bg: #FAF8F3;
  --surface: #FFFFFF;
  --surface-2: #F5F2E9;

  --ink: #1B1813;
  --ink-2: #605949;
  --ink-3: #696153;

  --line: #EAE4D6;
  --line-2: #D9D0BC;

  /* antique gold, darkened until it is legible as text; the true gold is
     kept for decorative gradients only */
  --accent: #7A5C0C;
  --accent-bright: #C9A227;
  --accent-soft: #FAF2DB;
  --accent-edge: #DBC287;

  /* Stanford Cardinal — identity and distinction */
  --signal: #8C1515;
  --signal-soft: #F8E7E4;
  --signal-edge: #DDB0AB;

  /* the "black" half of black-and-gold — software, not research output */
  --mark: #2A2520;
  --mark-soft: #EFEBE2;

  --shadow-tint: 27, 24, 19;
  --accent-tint: 122, 92, 12;
  --header-bg: rgba(250, 248, 243, 0.82);

  --wash-1: rgba(201, 162, 39, 0.10);
  --wash-2: rgba(140, 21, 21, 0.05);
  --wash-3: rgba(27, 24, 19, 0.045);

  --font-display: 'Plus Jakarta Sans', 'Inter', system-ui, sans-serif;
  --font-sans: 'Inter', -apple-system, BlinkMacSystemFont, 'Segoe UI', sans-serif;
  --font-mono: 'JetBrains Mono', 'IBM Plex Mono', Consolas, monospace;

  /* 4px base; --space-1 (4px) is unused and therefore not defined */
  --space-2: 8px;  --space-3: 12px; --space-4: 16px;
  --space-5: 24px; --space-6: 32px; --space-7: 48px; --space-8: 64px; --space-9: 96px;

  --r-sm: 6px;
  --r-md: 10px;
  --r-lg: 14px;
  --r-pill: 999px;

  --content-max: min(1360px, 93vw);
  --nav-height: 62px;

  --t-fast: 140ms ease;

  /* elevation derives from the ink tint, so shadows never look grey-blue */
  --shadow-1: 0 1px 2px rgba(var(--shadow-tint), 0.05), 0 1px 3px rgba(var(--shadow-tint), 0.03);
  --shadow-2: 0 2px 4px rgba(var(--shadow-tint), 0.05), 0 10px 24px -14px rgba(var(--shadow-tint), 0.16);
  --shadow-accent: 0 4px 14px -6px rgba(var(--accent-tint), 0.26);
}

@media (max-width: 959px) { :root { --nav-height: 56px; } }

/* -------------------------------- reset --------------------------------- */

*, *::before, *::after { box-sizing: border-box; }

html { scroll-behavior: smooth; -webkit-text-size-adjust: 100%; }

body {
  margin: 0;
  background: var(--bg);
  color: var(--ink);
  font-family: var(--font-sans);
  font-size: 16px;
  line-height: 1.5;
  -webkit-font-smoothing: antialiased;
  text-rendering: optimizeLegibility;
  overflow-x: hidden;
}

h1, h2, h3 { margin: 0; font-family: var(--font-display); font-weight: 700; letter-spacing: -0.01em; }
p { margin: 0; }
ul { margin: 0; padding: 0; list-style: none; }
img { max-width: 100%; display: block; }
a { color: inherit; text-decoration: none; }

a.inline-link {
  color: var(--ink);
  text-decoration: underline;
  text-decoration-color: var(--accent-edge);
  text-decoration-thickness: 1.5px;
  text-underline-offset: 3px;
  transition: color var(--t-fast), text-decoration-color var(--t-fast);
}
a.inline-link:hover, a.inline-link:focus-visible {
  color: var(--accent);
  text-decoration-color: var(--accent);
}

:focus-visible { outline: 2px solid var(--accent); outline-offset: 3px; border-radius: 2px; }

@media (prefers-reduced-motion: reduce) {
  html { scroll-behavior: auto; }
  *, *::before, *::after { transition-duration: 0.01ms !important; animation-duration: 0.01ms !important; }
}

/* --------------------------- airy background ---------------------------- */
/* Three very diffuse colour washes keep the page feeling light rather than
   plain — no texture, no noise. */

.bg-wash {
  position: fixed;
  inset: 0;
  z-index: -2;
  pointer-events: none;
  background:
    radial-gradient(760px 460px at 12% -6%, var(--wash-1), transparent 68%),
    radial-gradient(680px 420px at 92% 2%, var(--wash-2), transparent 70%),
    radial-gradient(900px 560px at 60% 104%, var(--wash-3), transparent 72%);
}

.avatar-watermark {
  position: fixed;
  inset: 0;
  z-index: -1;
  pointer-events: none;
  background: url('../images/ZhuoZheng.png') center/contain no-repeat;
  filter: grayscale(1) blur(20px) brightness(1.1);
  transform: scale(1.14);
  opacity: 0;
  transition: opacity 600ms ease-in-out;
}
html[data-silhouette='on'] .avatar-watermark { opacity: 0.07; }

/* -------------------------------- layout -------------------------------- */

.wrap {
  max-width: var(--content-max);
  margin: 0 auto;
  padding: 0 clamp(18px, 4vw, 44px);
}

.section {
  margin-top: var(--space-9);
  scroll-margin-top: calc(var(--nav-height) + var(--space-4));
}
@media (max-width: 959px) { .section { margin-top: var(--space-8); } }

.section-head {
  padding-bottom: var(--space-3);
  border-bottom: 1px solid var(--line);
  margin-bottom: var(--space-6);
}

.section-title {
  font-family: var(--font-display);
  font-size: clamp(20px, 2.3vw, 26px);
  font-weight: 700;
  color: var(--ink);
}

/* --------------------------------- nav ---------------------------------- */

.site-header {
  position: sticky;
  top: 0;
  z-index: 100;
  height: var(--nav-height);
  background: var(--header-bg);
  backdrop-filter: blur(14px) saturate(150%);
  -webkit-backdrop-filter: blur(14px) saturate(150%);
  border-bottom: 1px solid var(--line);
}

.nav-inner {
  max-width: var(--content-max);
  margin: 0 auto;
  padding: 0 clamp(18px, 4vw, 44px);
  height: 100%;
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: var(--space-5);
}

.nav-word {
  font-family: var(--font-display);
  font-size: 15px;
  font-weight: 700;
  letter-spacing: -0.01em;
  color: var(--signal);
  flex-shrink: 0;
}

.nav-links {
  position: relative;
  display: flex;
  align-items: center;
  gap: var(--space-2);
  height: 100%;
}

/* pill-shaped nav items — the friendly, fresh cue */
.nav-item {
  display: flex;
  align-items: baseline;
  gap: 5px;
  padding: 7px 11px;
  border-radius: var(--r-pill);
  white-space: nowrap;
  transition: background var(--t-fast), color var(--t-fast);
}
.nav-index {
  font-family: var(--font-mono);
  font-size: 9.5px;
  color: var(--ink-3);
  transition: color var(--t-fast);
}
.nav-label {
  font-size: 12.5px;
  font-weight: 600;
  letter-spacing: 0.01em;
  color: var(--ink-2);
  transition: color var(--t-fast);
}
.nav-item:hover { background: var(--surface); box-shadow: var(--shadow-1); }
.nav-item:hover .nav-label { color: var(--ink); }

.nav-item.is-active { background: var(--accent-soft); }
.nav-item.is-active .nav-label { color: var(--accent); }
.nav-item.is-active .nav-index { color: var(--accent); opacity: 0.75; }

@media (max-width: 900px) {
  .nav-links {
    overflow-x: auto;
    scrollbar-width: none;
    -ms-overflow-style: none;
    mask-image: linear-gradient(to right, transparent 0, #000 14px, #000 calc(100% - 14px), transparent 100%);
    -webkit-mask-image: linear-gradient(to right, transparent 0, #000 14px, #000 calc(100% - 14px), transparent 100%);
  }
  .nav-links::-webkit-scrollbar { display: none; }
}

/* --------------------------------- hero --------------------------------- */

.hero { padding-top: var(--space-6); }

.hero-grid {
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: var(--space-5);
}

.hero-photo-col {
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: var(--space-4);
  flex-shrink: 0;
}

.hero-photo-img {
  width: clamp(104px, 14vh, 136px);
  height: clamp(104px, 14vh, 136px);
  border-radius: 50%;
  object-fit: cover;
  border: 3px solid var(--surface);
  box-shadow: var(--shadow-2);
}

.social-row { display: flex; justify-content: center; gap: var(--space-2); }
.social-row a {
  width: 32px; height: 32px;
  display: grid;
  place-items: center;
  font-size: 14px;
  color: var(--ink-2);
  background: var(--surface);
  border: 1px solid var(--line);
  border-radius: 50%;
  box-shadow: var(--shadow-1);
  transition: color var(--t-fast), border-color var(--t-fast), transform var(--t-fast), box-shadow var(--t-fast);
}
.social-row a:hover, .social-row a:focus-visible {
  color: var(--accent);
  border-color: var(--accent-edge);
  transform: translateY(-2px);
  box-shadow: var(--shadow-accent);
}

.hero-intro { width: 100%; text-align: center; }

.hero-name {
  font-family: var(--font-display);
  font-size: clamp(28px, 4vh, 42px);
  font-weight: 700;
  line-height: 1.1;
  letter-spacing: -0.02em;
  color: var(--ink);
}

.hero-affiliation {
  margin-top: var(--space-2);
  font-size: clamp(13.5px, 1.6vh, 15.5px);
  color: var(--ink-2);
}
/* the institution reads in Cardinal, like the name above it */
.hero-affiliation .inline-link { text-decoration-color: var(--signal-edge); }
.hero-affiliation .inline-link:hover,
.hero-affiliation .inline-link:focus-visible {
  color: var(--signal);
  text-decoration-color: var(--signal);
}

.hero-divider {
  width: 34px;
  height: 3px;
  border-radius: var(--r-pill);
  background: linear-gradient(to right, var(--signal), var(--accent-bright));
  margin: var(--space-4) auto;
}

.hero-body { width: 100%; }

.hero-body .prose {
  /* name/affiliation stay centred on narrow screens, but body copy never
     does — centred paragraphs are hard to read */
  text-align: left;
  font-size: clamp(13.5px, 1.68vh, 15.5px);
  line-height: 1.66;
  color: var(--ink-2);
}
.hero-body .prose strong { color: var(--ink); font-weight: 600; }
.hero-body .prose + .prose { margin-top: var(--space-3); }

/* the highest-value line on the page, so it carries the signal colour */
.job-market-callout {
  margin-top: var(--space-4);
  display: block;
  text-align: left;
  background: var(--signal-soft);
  border: 1px solid var(--signal-edge);
  border-radius: var(--r-md);
  padding: 11px var(--space-4);
  font-size: clamp(12.5px, 1.55vh, 14.5px);
  font-weight: 600;
  color: var(--signal);
}

.hero-email {
  margin-top: var(--space-3);
  font-family: var(--font-mono);
  font-size: clamp(11px, 1.35vh, 12.5px);
  color: var(--ink-3);
}

@media (min-width: 780px) {
  .hero-grid {
    flex-direction: row;
    align-items: flex-start;
    justify-content: center;
    gap: var(--space-6);
    max-width: 1120px;
    margin: 0 auto;
  }
  .hero-photo-col { position: sticky; top: calc(var(--nav-height) + var(--space-4)); }
  .hero-intro { text-align: left; flex: 1; min-width: 0; }
  .hero-divider { margin: var(--space-4) 0; }
  .hero-body .prose { text-align: justify; text-justify: inter-word; hyphens: auto; }
}

/* ------------------ change family: research threads --------------------- */
/* Each thread leads with a claim; the works are evidence chips under it.
   Synthesis, not another enumeration of the publication list below. */

.threads {
  display: grid;
  grid-template-columns: 1fr;
  gap: var(--space-4);
}

@media (min-width: 900px) {
  .threads { grid-template-columns: 1fr 1fr; gap: var(--space-5); }
  /* the software coda spans the full row — it is infrastructure, not a thread */
  .thread-tool { grid-column: 1 / -1; }
}

.thread {
  background: var(--surface);
  border: 1px solid var(--line);
  border-radius: var(--r-lg);
  box-shadow: var(--shadow-1);
  padding: var(--space-5);
  transition: box-shadow var(--t-fast), border-color var(--t-fast);
}
.thread:hover { box-shadow: var(--shadow-2); border-color: var(--accent-edge); }

.thread-head {
  display: flex;
  align-items: center;
  gap: var(--space-3);
  margin-bottom: var(--space-3);
}

.thread-idx {
  flex-shrink: 0;
  display: grid;
  place-items: center;
  width: 26px;
  height: 26px;
  border-radius: 8px;
  background: var(--accent-soft);
  color: var(--accent);
  font-family: var(--font-mono);
  font-size: 11px;
  font-weight: 500;
}

.thread-name {
  font-family: var(--font-display);
  font-size: 16.5px;
  font-weight: 700;
  line-height: 1.25;
  color: var(--ink);
}

.thread-claim {
  font-size: 14px;
  line-height: 1.6;
  color: var(--ink-2);
}
.thread-claim strong {
  color: var(--ink);
  font-weight: 600;
  background: linear-gradient(to top, var(--accent-soft) 42%, transparent 42%);
}

.thread-works {
  margin-top: var(--space-4);
  display: flex;
  flex-wrap: wrap;
  gap: var(--space-2);
}

/* evidence chip: method name + where it landed */
.work-chip {
  display: inline-flex;
  align-items: baseline;
  gap: 7px;
  padding: 5px 11px;
  background: var(--bg);
  border: 1px solid var(--line-2);
  border-radius: var(--r-pill);
  transition: color var(--t-fast), border-color var(--t-fast), background var(--t-fast), transform var(--t-fast);
}
.work-chip:hover, .work-chip:focus-visible {
  background: var(--accent-soft);
  border-color: var(--accent-edge);
  transform: translateY(-1px);
}

.work-name {
  font-family: var(--font-display);
  font-size: 13px;
  font-weight: 600;
  color: var(--ink);
}
.work-chip:hover .work-name { color: var(--accent); }

.work-venue {
  font-family: var(--font-mono);
  font-size: 10px;
  letter-spacing: 0.03em;
  color: var(--ink-3);
}

.work-star { font-size: 9px; color: var(--signal); align-self: center; }

/* one compact line of external evidence per thread */
.thread-impact {
  margin-top: var(--space-3);
  padding-top: var(--space-3);
  border-top: 1px dashed var(--line-2);
  font-size: 12.5px;
  line-height: 1.5;
  color: var(--ink-3);
}
.thread-impact > i { color: var(--accent); margin-right: 6px; font-size: 11px; }

.thread-tool .thread-idx { background: var(--mark-soft); color: var(--mark); }
.thread-tool .work-name i { margin-right: 5px; color: var(--ink-2); }

/* --------------------------------- news --------------------------------- */

.news-list { display: flex; flex-direction: column; gap: var(--space-2); }

.news-row {
  display: grid;
  grid-template-columns: 84px 1fr;
  gap: var(--space-4);
  padding: 12px var(--space-3);
  border-radius: var(--r-md);
  transition: background var(--t-fast);
}
.news-row:hover { background: var(--surface); box-shadow: var(--shadow-1); }

@media (max-width: 520px) {
  .news-row { grid-template-columns: 1fr; gap: 3px; }
}

.news-date {
  font-family: var(--font-mono);
  font-size: 11.5px;
  color: var(--accent);
  padding-top: 2px;
}

.news-body {
  font-size: 14.5px;
  line-height: 1.6;
  color: var(--ink-2);
}
.news-body strong { color: var(--ink); font-weight: 600; }
.news-flag { color: var(--signal); font-size: 11px; margin-right: var(--space-2); }

/* ----------------------------- publications ----------------------------- */

.pub-list { display: flex; flex-direction: column; }

.pub-entry {
  display: grid;
  grid-template-columns: 38px 1fr;
  gap: var(--space-4);
  padding: var(--space-3);
  border-radius: var(--r-md);
  border-top: 1px solid var(--line);
  transition: background var(--t-fast), box-shadow var(--t-fast);
}
.pub-entry:first-child { border-top: none; }
.pub-entry:hover { background: var(--surface); box-shadow: var(--shadow-1); }

@media (max-width: 720px) {
  .pub-entry { grid-template-columns: 1fr; }
  .pub-num { display: none; }
}

.pub-num {
  font-family: var(--font-mono);
  font-size: 12.5px;
  color: var(--ink-3);
  padding-top: 2px;
}

.pub-meta {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  gap: var(--space-2);
  font-size: 12px;
  color: var(--ink-3);
}

/* rounded accent pill for the venue — no uppercase transform, so venue
   names keep their own casing (NeurIPS, arXiv, ISPRS P&RS) */
.venue-badge {
  display: inline-block;
  background: var(--accent-soft);
  border: 1px solid var(--accent-edge);
  border-radius: var(--r-pill);
  padding: 2px 9px;
  font-family: var(--font-mono);
  font-size: 10.5px;
  font-weight: 500;
  letter-spacing: 0.04em;
  color: var(--accent);
}

.pub-title {
  margin-top: 3px;
  font-family: var(--font-display);
  font-weight: 600;
  font-size: 16px;
  line-height: 1.32;
  color: var(--ink);
}
@media (max-width: 599px) { .pub-title { font-size: 15.5px; } }

.pub-authors {
  margin-top: 2px;
  font-size: 13px;
  line-height: 1.42;
  color: var(--ink-2);
}
/* the site owner's name, so it is findable in every author list */
.pub-authors strong { color: var(--signal); font-weight: 600; }

.pub-quote {
  margin-top: 6px;
  padding: 5px 10px;
  background: var(--surface-2);
  border-radius: var(--r-sm);
  font-size: 12.5px;
  line-height: 1.45;
  color: var(--ink-2);
}
.pub-quote strong { color: var(--ink); font-weight: 600; }

.pub-tags {
  margin-top: 6px;
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  gap: 6px;
}

/* soft outlined chips */
.resource-tag {
  display: inline-flex;
  align-items: center;
  gap: 5px;
  padding: 2px 9px;
  background: var(--surface);
  border: 1px solid var(--line-2);
  border-radius: var(--r-pill);
  font-family: var(--font-mono);
  font-size: 10px;
  font-weight: 500;
  letter-spacing: 0.04em;
  text-transform: uppercase;
  color: var(--ink-2);
  transition: color var(--t-fast), border-color var(--t-fast), background var(--t-fast);
}
.resource-tag i { font-size: 10px; }
.resource-tag:hover, .resource-tag:focus-visible {
  color: var(--accent);
  border-color: var(--accent-edge);
  background: var(--accent-soft);
}

.badge-row { margin-top: var(--space-2); display: flex; flex-wrap: wrap; gap: var(--space-2); }

/* the recognition marker — distinct from the accent on purpose */
.badge-fill {
  display: inline-flex;
  align-items: center;
  gap: 5px;
  background: var(--signal-soft);
  border: 1px solid var(--signal-edge);
  color: var(--signal);
  border-radius: var(--r-pill);
  padding: 2px 9px;
  font-family: var(--font-mono);
  font-size: 9.5px;
  font-weight: 500;
  letter-spacing: 0.05em;
  text-transform: uppercase;
}

.adopt-note, .result-note {
  margin-top: var(--space-2);
  font-size: 12.5px;
  line-height: 1.5;
  color: var(--ink-3);
}
.adopt-note > i, .result-note > i { color: var(--signal); margin-right: 5px; font-size: 10px; }
.result-note strong { color: var(--ink-2); font-weight: 600; }

/* ------------------------------- teaching ------------------------------- */

.teaching-list { display: flex; flex-direction: column; gap: var(--space-2); }
.teaching-list li { font-size: 14.5px; color: var(--ink-2); }
.teaching-list strong { color: var(--ink); font-weight: 600; }

/* -------------------------------- honors -------------------------------- */

.award-group { margin-top: var(--space-6); }
.award-group:first-child { margin-top: 0; }

/* shared group header (honors + academic service) */
.group-label {
  display: flex;
  align-items: center;
  gap: var(--space-2);
  margin-bottom: var(--space-3);
}
.group-label::before {
  content: '';
  width: 16px; height: 3px;
  border-radius: var(--r-pill);
  background: linear-gradient(to right, var(--accent), var(--accent-bright));
  flex-shrink: 0;
}
.group-label span {
  font-family: var(--font-mono);
  font-size: 10.5px;
  font-weight: 500;
  letter-spacing: 0.1em;
  text-transform: uppercase;
  color: var(--ink-2);
}

.awards-list { display: flex; flex-direction: column; gap: var(--space-2); }

.award-row {
  display: grid;
  grid-template-columns: 26px 1fr;
  gap: var(--space-3);
  padding: var(--space-4) var(--space-3);
  border-radius: var(--r-md);
  background: var(--surface);
  border: 1px solid var(--line);
  box-shadow: var(--shadow-1);
  transition: transform var(--t-fast), box-shadow var(--t-fast);
}
.award-row:hover { transform: translateY(-1px); box-shadow: var(--shadow-2); }
.award-row > i { color: var(--signal); font-size: 13px; padding-top: 3px; }

.award-title {
  font-family: var(--font-display);
  font-weight: 600;
  font-size: 14.5px;
  line-height: 1.4;
  color: var(--ink);
}
.award-team { margin-top: 3px; font-size: 12.5px; line-height: 1.5; color: var(--ink-3); }

.award-links { margin-top: var(--space-2); display: flex; flex-wrap: wrap; gap: var(--space-4); }
.award-links a {
  font-family: var(--font-mono);
  font-size: 10.5px;
  letter-spacing: 0.06em;
  text-transform: uppercase;
  color: var(--ink-2);
  transition: color var(--t-fast);
}
.award-links a:hover, .award-links a:focus-visible { color: var(--accent); }
.award-links i { font-size: 9px; margin-right: 4px; }

/* -------------------------------- talks --------------------------------- */

.talks-list { display: flex; flex-direction: column; gap: var(--space-2); }

.talk-row {
  display: grid;
  grid-template-columns: 84px 1fr;
  gap: var(--space-4);
  padding: var(--space-3);
  border-radius: var(--r-md);
  transition: background var(--t-fast), box-shadow var(--t-fast);
}
.talk-row:hover { background: var(--surface); box-shadow: var(--shadow-1); }

@media (max-width: 620px) {
  .talk-row { grid-template-columns: 1fr; gap: 3px; }
}

.talk-date {
  font-family: var(--font-mono);
  font-size: 11.5px;
  color: var(--accent);
  padding-top: 2px;
}
.talk-venue { font-size: 12.5px; line-height: 1.4; color: var(--ink-3); }
.talk-title {
  margin-top: 3px;
  font-family: var(--font-display);
  font-weight: 600;
  font-size: 14.5px;
  line-height: 1.4;
  color: var(--ink);
}
.talk-award { margin-left: var(--space-2); vertical-align: 1px; }

/* ------------------------------- service -------------------------------- */

.service-group { margin-top: var(--space-6); }
.service-group:first-child { margin-top: 0; }

.service-simple { display: flex; flex-direction: column; gap: var(--space-2); }
.service-simple li { font-size: 14.5px; color: var(--ink-2); }
.service-simple i { font-size: 11px; margin-left: 5px; color: var(--ink-3); }

.service-runin {
  font-size: 13.5px;
  line-height: 1.9;
  color: var(--ink-2);
}
.service-runin .sep { color: var(--line-2); margin: 0 var(--space-2); }
.service-runin .yr { font-family: var(--font-mono); font-size: 11.5px; color: var(--ink-3); }

/* -------------------------------- footer -------------------------------- */

.site-footer {
  margin-top: var(--space-9);
  padding: var(--space-5) 0 var(--space-8);
  border-top: 1px solid var(--line);
  display: flex;
  justify-content: space-between;
  align-items: center;
  gap: var(--space-4);
  flex-wrap: wrap;
}
.site-footer p, .back-to-top {
  font-family: var(--font-mono);
  font-size: 11px;
  letter-spacing: 0.06em;
  color: var(--ink-3);
}
.back-to-top { transition: color var(--t-fast); }
.back-to-top:hover, .back-to-top:focus-visible { color: var(--accent); }